1. Field of the Invention
The present invention relates to a cage that holds a rolling element while allowing said rolling element to rotate freely, and a rolling guide unit on which said cage is equipped.
2. Description of the Prior Art
FIGS. 1 and 2 indicate a rolling guide unit for linear motion of the prior art equipped with a cage (to be referred to as a linear motion rolling guide unit). Furthermore, this linear motion rolling guide unit is disclosed in Japanese Examined Utility Model Publication No. 64-6407.
As indicated in FIG. 1, said linear motion rolling guide unit has bed 1 and table 2. The cross-sections of bed 1 and table 2 are each formed into the shape of the letter "U", and track grooves 1a and 2a are formed in the lengthwise direction in the outside and inside of bed 2 and table 2, respectively. Bed 1 is arranged to be on the inside of table 2 so that these track grooves 1a and 2a are opposing each other.
A rectangular plate-shaped cage 3, made of a material such as synthetic resin or the like, is juxtaposed between said track grooves 1a and 2a. As is also indicated in FIG. 2, a plurality of openings 3a are provided in a row in this cage 3, and rolling elements in the form of balls 4 are inserted through each of said openings 3a. These balls 4 roll over said track grooves 1a and 2a accompanying relative movement of bed 1 and table 2.
However, diameter D.sub.2 of the edges of openings 3a, formed in cage 3 for insertion of balls 4, is formed slightly smaller than the diameter of balls 4. This arrangement is referred to as a rolling element holding system. As a result of being composed in this manner, cage 3 is positioned by each ball 4 and not allowed to move horizontally to the left and right. This prevents an increase in sliding resistance caused by full surface contact of said cage 3 with bed 1 and table 2. However, as indicated by the double dash broken line in FIG. 2, since cage 3 is able to rotate about the center of the axis that passes through each ball 4, there are cases wherein the corners of both its upper and lower edges make contact with bed 1 and table 2. However, since this contact is only in the form of linear contact, it does not become a major obstruction to obtaining a smooth sliding state.
However, since said cage 3 is formed into a thin plate, there is the problem of it being easy for balls 4 to come out of cage 3.
Therefore, a cage 3 was proposed as indicated in FIGS. 3 and 4. Furthermore, this cage 3 is also disclosed in Japanese Examined Utility Model Publication No. 64-6407.
As indicated in FIGS. 3 and 4, arc-shaped projections 3b are formed into a single structure in the state of protruding from the primary surfaces in this cage 3 so as to face openings 3a wherein balls 4 are inserted. These projections 3b serve to prevent balls 4 from coming out of openings 3a.
In the linear motion rolling guide unit of the prior art described above, cage 3, which is formed into a relatively thin plate, is easily subjected to warping. There are cases wherein the relative operating states of bed 1 and table 2 are obstructed by this warping. In addition, since projections 3b are formed over nearly the entire circumference of openings 3a, there is the additional disadvantage of increased slipping resistance with balls 4.